A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In such a case, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g. including part of, one, or several dies) on a substrate (e.g. a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Conventional lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at once, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.
Applying the desired pattern on the substrate with high accuracy may allow smaller features to be patterned, which allows smaller integrated circuits with more functionality. Further, patterning with high accuracy may improve the amount of properly functioning ICs produced per substrate.
To achieve high accuracy patterning, some components in the lithographic apparatus need to have an accurately determined position, size or shape.
For example, known lithographic apparatus comprise movable stage systems to move objects with relatively high speed and accuracy. Examples of these movable stage systems are a movable substrate support configured to support a substrate and a patterning device support configured to support a patterning device.
Actuator systems are used to actuate the movable part of the stage system with respect to another part of the actuator system. In some embodiment the other part may also be a movable part.
For example, in a known movable stage system, in particular a substrate support, the stage comprises a long stroke part and a short stroke part. The long stroke part is arranged on a base frame and configured to movably support the short stroke module. The short stroke part is configured to support a substrate. The short stroke part can be positioned with high accuracy over a relatively small range of movement with respect to the long stroke part. The long stroke part can be moved over a relatively large range of movement with respect to the base frame, but with a relatively low accuracy.
The actuator system may comprise a motor and a mover element movable by the motor. The motor may for example be mounted on the long stroke part and the mover element may be part of the short stroke part. The motor comprises a coil which may heat during use of the motor. The heat generated by the coil may negatively influence the performance a lithographic apparatus, in particular caused by the heat being transferred to the mover element. To decrease the effect of this heat, a coil fluid cooling system is provided, which fluid cooling system is configured to cool the coil using a cooling fluid.
In an implementation, the coil fluid cooling system is an active fluid cooling system which uses a two-temperature mixture to adjust the temperature of the cooling fluid of the fluid cooling system. This allows cooling of the coil. However, the cooling may have some time lag, in particular when there is some distance between the coil and the mixing location of the two-temperature mixture. This results in a relative slow type of control having a low bandwidth.
Other types of components that generate heat may be electrical components such as sensors, and may be optical components that are heated due to exposure to radiation. The heat generated by these components may be transferred to components that change position, size or shape due to an increase in temperature. These changes may deteriorate the accuracy of the lithographic apparatus.